E positively associated with tumor grade and ESR1, PGR, and ESR2 steroid hormone receptor expression level and negatively associated with invasive epithelial tumor cell content and tumor size. In addition, ESR2 was more highly expressed in tumors with a higher percentage of stromal cells (786 tumors with 30 to 70 invasive epithelial cells), and ESR1 wasSieuwerts et al. Breast Cancer Research 201